linux-kernel - Re: [PATCH 2/2] arm64: dts: meson: libretech-cc: switch eMMC to 1.8v

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Date:   Wed, 02 Jan 2019 11:51:19 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Kevin Hilman <khilman@...libre.com>,
        Carlo Caione <carlo@...one.org>, devicetree@...r.kernel.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: dts: meson: libretech-cc: switch eMMC to 1.8v

On Sat, 2018-12-22 at 18:01 +0100, Martin Blumenstingl wrote:
> Hi Jerome,
> 
> On Thu, Dec 20, 2018 at 5:11 PM Jerome Brunet <jbrunet@...libre.com> wrote:
> > While some 3.3v eMMC 4.0 are available from libretech, the default
> > option for the aml-s905x-cc seems to 1.8v 5.0 modules.
> nit-pick:
> can you please state which module (storage size) you used for testing?
> you probably still remember that we had some confusion on Odroid-C2
> which eMMC module works and which doesn't, so let's be explicit here
> 
> > Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
> > ---
> >  .../boot/dts/amlogic/meson-gxl-s905x-libretech-cc.dts    | 9 +++++----
> >  1 file changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm64/boot/dts/amlogic/meson-gxl-s905x-libretech-cc.dts
> > b/arch/arm64/boot/dts/amlogic/meson-gxl-s905x-libretech-cc.dts
> > index daad007fac1f..d0d202cf7161 100644
> > --- a/arch/arm64/boot/dts/amlogic/meson-gxl-s905x-libretech-cc.dts
> > +++ b/arch/arm64/boot/dts/amlogic/meson-gxl-s905x-libretech-cc.dts
> > @@ -118,8 +118,8 @@
> >         vddio_boot: regulator-vddio_boot {
> >                 compatible = "regulator-fixed";
> >                 regulator-name = "VDDIO_BOOT";
> > -               regulator-min-microvolt = <3300000>;
> > -               regulator-max-microvolt = <3300000>;
> > +               regulator-min-microvolt = <1800000>;
> > +               regulator-max-microvolt = <1800000>;
> is there a 3.3V -> 1.8V regulator on the eMMC module?
> I'm not sure about the schematics but it seems to be that the board
> itself supplies only 3.3V to the eMMC connector, so I'm not sure where
> 1.8V come from in this case

The module is indeed fed by 3.3v only but it has embedded LDOs add will feed
back the supply of the BOOT gpio bank.

I tried the following modules:
* 8 GB samsung - v1.0-170420
* 32 GB toshiba - v1.0-170421

I think you can't get them here [0].

In theory, these 4.x modules [1] could also work. They don't have the LDOs and
are directly feeding back the 3.3v to the BOOT bank. Since the modules are
advertised as being compatible with the Allwinner boards only, and not the AML
ones, it should not be the default option.

[0] : 
https://www.loverpi.com/collections/libre-computer-project/products/libre-computer-board-emmc-5-x-module?variant=4173557729
[1] : 
https://www.loverpi.com/collections/libre-computer-project/products/libre-computer-board-emmc-4-x-module?variant=761282232333

> can you please add a comment to the .dts about this?

Sure

> 
> 
> Regards
> Martin